Phencyclidine, one of the major drugs of abuse, has been the focus of significant research since the discovery of a specific receptor in the brain. The receptor is included in the complex excitatory amino acid ion channel. There are three structural classes of compounds which apparently bind to this same receptor and act as noncompetitive antagonists to N-methyl-D-asparte (NMDA) binding {dibenzocycloheptenimines (MK-801); arylcyclohexylpiperidines (PCP, TCP); and dioxolanes (dexoxadrol)}. We and others have explored the preparation of analogues labeled with the positron-emitting radioisotope, F-18, and attempted to imaging the receptor in vivo using positron emission tomography. Initial in vivo studies of [3H]fluorothienyl-cyclohexylpiperidine (FTCP) indicated that the ligand had promise as a marker of NMDA receptor physiology. Unfortunately, our attempt to utilize [18F]FTCP indicated that higher affinity and/or lower lipophilicity would be required for further evaluation in positron emission tomography. We wished to evaluate other analogs of phencyclidine with fluorine substitution in the piperidine ring. Since, the 3,4-didehydro TCP has been the highest affinity compound of this chemical class reported to date [Ki=12 nM, Rice personal communication]. We have synthesized vinyl fluoride derivatives of PCP and TCP and completed in vitro equilibrium binding experiments. A manuscript is in preparation to report our results. When this manuscript is completed the project will be completed.